This invention relates to a process for fractionating milk and/or milk products, particularly permeate from the ultrafiltration of whey or the mother liquor from lactose crystallization.
In addition to its main constituent, water, milk contains fat, protein, lactose, mineral substances and a nitrogen-containing, non-protein-containing fraction, the so-called "NPN fraction". The NPN fraction (NPN means non-proteinaceous nitrogen) essentially consists of amino acids, urea, creatinine and ammonia.
Part of the milk supply is processed in dairies into milk for drinking, if necessary after purification, skimming, pasteurization or sterilization. The remaining portion of the milk is processed further to separate certain fractions. Some processes permit selective separation of individual fractions. Other processes aim at completely separating out the substances contained therein.
One modern method of fractionating milk or milk products is ultrafiltration. Ultrafiltration yields a retentate enriched in proteins and a permeate which contains enriched amounts of salts, lactose, the NPN fraction and riboflavin. Ultrafiltration can therefore be used for enriching the salts, lactose, the NPN fraction and riboflavin from milk or milk products. The permeate solution can, for instances, be dried to yield salt-containing and lactose-containing permeats powder. On the other hand, lactose can be obtained from the permeate solution by fractional crystallization.
The desalting of skimmed milk or milk products such as whey, or permeate solution from ultrafiltration is likewise a known process for fractionating milk or milk products. The desalting can for instance take place by passing the aforementioned aqueous substrate over an ion exchanger. Another possibility is electrodialytic treatment of the substrates. The purpose of this desalting is to produce dietetic milk or dietatic milk products. Furthermore, desalting offers certain process-related advantages. For instance, it is known that lactose crystallizes better from desalted aqueous solution. Another example is the separation of whey proteins from whey, which is known to be possible substantially quantitatively from desalted whey by means of acid/heat precipitation. It has also been established that desalted substrate solutions have a higher throughput rate in ultrafiltration.
The known processes for fractionating milk or milk products are therefore carried out in aqueous solution. However, milk and milk products in this form are readily perishable and therefore must be processed promptly. Therefore, when carrying out the known fractionation processes, one is tied to the location where the milk products are produced, that is to say, the dairy. Furthermore, there is seasonal dependency. Although milk or milk products could be dried and then redissolved in water for fractionation by known processes, this is laborious and involves high water and energy consumption.